1. Field of the Invention
This invention relates generaly to apparatus for feeding of sheets seriatim from a sheet supply stack, and more particularly to a sheet feeding apparatus having a unidirectionally rotating scuff feeder and a counter-rotating reverse buckle inducing roller.
2. Description of the Prior Art
In modern reproduction equipment, such as printers or electrophotographic copiers, it is common practice to feed sheets seriatim from a sheet supply stack to a reproduction station at which an image is applied to such sheets. A typical apparatus for seriatim feeding of sheets includes a rotating roller with a peripheral surface having a high coefficient of friction. The rotating roller is brought into contact with a sheet in the supply stack (either the top-most or bottom-most sheet) and frictionally drives the sheet from the stack into a transport for delivery to the reproduction station. Such friction feeding apparatus is referred to in the art as a scuff feeder.
While scuff feeders have found general acceptance for seriatim feeding of sheets, these feeders have a tendency to feed several sheets at one time. Further, they may prematurely feed subsequent sheets (after the fed sheet passes from control of the feeder), or may interfere with movement of the sheet when it is being fed by the downstream transport. Multiple sheet feeds, of course, are undesirable because they tend to jam in the downstream transports, causing machine shut-down, and waste non-imprinted sheets. In order to reduce the frequency of such multiple feeds, a technique called reverse buckle feeding was devised.
Reverse buckle feeding, as described for example in U.S. Pat. No. 3,944,215, issued Mar. 16, 1976 in the name of Beck, involves separating a sheet from the supply stack by first urging such sheet in a direction opposite to the direction of feed against a marginal support. Because the marginal edge of the sheet is restrained by the support, such urging causes the sheet to buckle transverse to the direction of travel thus separating that portion of the sheet from subsequent sheets in the supply stack. The buckled sheet is then fed in the feeding direction free of subsequent sheets which might otherwise have been tacked to the fed sheet. While reverse buckle feeding reduces multiple sheet feeds, it generally requires complex control of the scuff feeder in order to accomplish the multiple-direction feeding actions. Further, the problem of premature feeding of subsequent sheets or interference with downstream transport of a sheet by the scuff feeder is not addressed by reverse buckle scuff feeding.